futures_util/sink/
with_flat_map.rs

Help
1use core::fmt;
2use core::marker::PhantomData;
3use core::pin::Pin;
4use futures_core::ready;
5use futures_core::stream::{FusedStream, Stream};
6use futures_core::task::{Context, Poll};
7use futures_sink::Sink;
8use pin_project_lite::pin_project;
9
10pin_project! {
11    /// Sink for the [`with_flat_map`](super::SinkExt::with_flat_map) method.
12    #[must_use = "sinks do nothing unless polled"]
13    pub struct WithFlatMap<Si, Item, U, St, F> {
14        #[pin]
15        sink: Si,
16        f: F,
17        #[pin]
18        stream: Option<St>,
19        buffer: Option<Item>,
20        _marker: PhantomData<fn(U)>,
21    }
22}
23
24impl<Si, Item, U, St, F> fmt::Debug for WithFlatMap<Si, Item, U, St, F>
25where
26    Si: fmt::Debug,
27    St: fmt::Debug,
28    Item: fmt::Debug,
29{
30    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
31        f.debug_struct("WithFlatMap")
32            .field("sink", &self.sink)
33            .field("stream", &self.stream)
34            .field("buffer", &self.buffer)
35            .finish()
36    }
37}
38
39impl<Si, Item, U, St, F> WithFlatMap<Si, Item, U, St, F>
40where
41    Si: Sink<Item>,
42    F: FnMut(U) -> St,
43    St: Stream<Item = Result<Item, Si::Error>>,
44{
45    pub(super) fn new(sink: Si, f: F) -> Self {
46        Self { sink, f, stream: None, buffer: None, _marker: PhantomData }
47    }
48
49    delegate_access_inner!(sink, Si, ());
50
51    fn try_empty_stream(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Si::Error>> {
52        let mut this = self.project();
53
54        if this.buffer.is_some() {
55            ready!(this.sink.as_mut().poll_ready(cx))?;
56            let item = this.buffer.take().unwrap();
57            this.sink.as_mut().start_send(item)?;
58        }
59        if let Some(mut some_stream) = this.stream.as_mut().as_pin_mut() {
60            while let Some(item) = ready!(some_stream.as_mut().poll_next(cx)?) {
61                match this.sink.as_mut().poll_ready(cx)? {
62                    Poll::Ready(()) => this.sink.as_mut().start_send(item)?,
63                    Poll::Pending => {
64                        *this.buffer = Some(item);
65                        return Poll::Pending;
66                    }
67                };
68            }
69        }
70        this.stream.set(None);
71        Poll::Ready(Ok(()))
72    }
73}
74
75// Forwarding impl of Stream from the underlying sink
76impl<S, Item, U, St, F> Stream for WithFlatMap<S, Item, U, St, F>
77where
78    S: Stream + Sink<Item>,
79    F: FnMut(U) -> St,
80    St: Stream<Item = Result<Item, S::Error>>,
81{
82    type Item = S::Item;
83
84    delegate_stream!(sink);
85}
86
87impl<S, Item, U, St, F> FusedStream for WithFlatMap<S, Item, U, St, F>
88where
89    S: FusedStream + Sink<Item>,
90    F: FnMut(U) -> St,
91    St: Stream<Item = Result<Item, S::Error>>,
92{
93    fn is_terminated(&self) -> bool {
94        self.sink.is_terminated()
95    }
96}
97
98impl<Si, Item, U, St, F> Sink<U> for WithFlatMap<Si, Item, U, St, F>
99where
100    Si: Sink<Item>,
101    F: FnMut(U) -> St,
102    St: Stream<Item = Result<Item, Si::Error>>,
103{
104    type Error = Si::Error;
105
106    fn poll_ready(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
107        self.try_empty_stream(cx)
108    }
109
110    fn start_send(self: Pin<&mut Self>, item: U) -> Result<(), Self::Error> {
111        let mut this = self.project();
112
113        assert!(this.stream.is_none());
114        this.stream.set(Some((this.f)(item)));
115        Ok(())
116    }
117
118    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
119        ready!(self.as_mut().try_empty_stream(cx)?);
120        self.project().sink.poll_flush(cx)
121    }
122
123    fn poll_close(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
124        ready!(self.as_mut().try_empty_stream(cx)?);
125        self.project().sink.poll_close(cx)
126    }
127}
futures_util/sink/with_flat_map.rs

futures_util/sink/
with_flat_map.rs
